@noble
In my experience wax moth is a symptom of a weak and/or failing hive rather than the cause of it. A strong hive will keep wax moth at bay. A swarm will even take over a hive that has died out and been decimated by wax moth, clean it out and start anew and be perfectly healthy....it is the natural cycle of things in the wild. A swarm will move into a hollow tree, build comb and live there for multiple seasons extending the nest each year then eventually die out for whatever reason, wax moth and mice move in and utilise the comb etc, breaking some of it down, then come swarming season the following year or maybe even 2 or 3 years later, a new swarm moves in, cleans up and reuses whatever comb can be salvaged and strips out and rebuilds whatever cannot.
Are you sure it is wax moth and not small hive beetle as the larvae from that can be more destructive I believe.....we don't have small hive beetle in the UK yet, so I have no experience of that.
If you are sure it is wax moth, then I would not be overly concerned about the other colonies unless they have other issues and are also weak.
If you can take photos of the comb from the failed colony and post if on this thread, it might be possible to determine what they died from..... Was there any honey left and was there brood? Did you see any varroa fras ....it's small white deposits in the brood cells, particularly noticeable if you turn the frames upside down and look into the cells as it usually gets deposited on the top edge of the cells, so not so obvious when you look down on the frames. Queen failure is another common cause of decline. Did you find the queen? Were the bees head first in the cells? Were there lots of dead bees in the hive or very few? When was the last time you can be sure they were alive? Sometimes activity at the entrance is actually other bees robbing out the stores after a colony has died or is weak, so that can be misleading.
At least you have plenty of other colonies to restock this hive from in a couple of months time.
Regards
Barbara